This invention relates to a reciprocating air motor, and more particularly to an air motor with an anti-phase piston which cancels the vibrations of a drive piston to provide an air motor which is less vibrational, quieter and permits greater accuracy in its manipulation. In addition, this invention relates to the use of air cushions between the pistons and at their ends to cause a floating action to the pistons. An adjustable air space adjacent the anti-phase piston is also provided to permit optimizing the vibration cancellation. Furthermore, this invention contemplates reducing operational noise by muffling the sound of the reciprocating motor. The manufacturability of the motor is improved by utilizing structures which permit greater manufacturing tolerances.
In the field, of reciprocating air motors which are often referred to as pneumatic motors, there have been various motor designs aimed at reducing vibration. The effort to reduce vibration has mainly concentrated on pneumatic impact tools which transmit vibrations to an operator when the tool impacts a surface. Examples of pneumatic tools which generally transmit the full recoil reaction of the tool to the operator, are pneumatic chippers, tampers, jack-hammers, and the like.
Reciprocating air motors for saws, drills and the like, while they do not impart to the operator the large amplitude forces associated with the recoil reaction of impact tools, are nevertheless rendered less useful by the vibrations imparted to the operator. In particular the vibrations cause the operator to tire and require frequent rest periods, and in addition have relegated pneumatic saws to gross cutting operations since the vibrations have prevented fine detail cutting operations.
In U.S. Pat. No. 4,681,172, there is disclosed a vibration reducing cushioning device for use with a pneumatic impact tool. The cushioning is achieved by admitting air into a cushioning region to provide a first level of cushioning and then admitting air from the cushioning region into a second region to provide a second level of cushioning. Another example of a method of reducing vibration in a pneumatic impact tool is set forth in U.S. Pat. No. 3,456,744 in which a drive piston which impacts the tool is surrounded by a sleeve which moves in the opposite direction to offset the vibrations caused by the rebounding of the drive piston from the tool. A further example of a design for reducing vibrations in a pneumatic impact tool is described in U.S. Pat. No. 3,892,280 in which an additional piston or extension is added to a drive or hammer piston to reduce pressure fluctuations when the hammer piston and the housing move relative to one another.
While the aforementioned arrangements for reducing vibration in pneumatic tools have provided the reduced transmission of vibrations to a tool operator, still further improvements in reducing vibrations would be beneficial. These improvements would be particularly beneficial if they can be achieved together with reducing the noise level of the motor.